Process for cleaning contaminated mercury



United States Patent No Drawing.

The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

This is a continuation-in-part of US. patent application Serial No. 716,823, filed February 21, 1958, for Process for Cleaning Contaminated Mercury.

The present invention relates to a process for cleaning contaminated mercury and, more particularly, to a safe and inexpensive process for cleaning mercury without requiring the use of strong acids, distillation, or direct handling or exposure of the mercury, or complex techniques or skilled personnel in the cleaning process.

Under these conditions, prior to this invention, one of two alternate solutions could be adopted, both equally undesirable for comparable reasons. One solution has been to replace the contaminated mercury with new mercury, obviously an expensive expedient, particularly where large quantities are needed.

The other solution required the adoption of a known cleaning process. Hereotfore, the processes for cleaning mercury consisted of triple distilling and of treating the mercury with cyanides and strong acids, which always presents the danger of escaping mercury vapors or cyanide gases, creating hazards of handling and possible injury to personnel. Moreover, the materials and apparatus used in the prior cleaning processes were relatively expensive and required skilled personnel to practice the processes. Where large quantities of contaminated mercury were involved, the cost of reclamation usually was found prohibitive to the extent that replacement of the contaminated mercury with new mercury was more economically desirable.

The process of the present invention contemplates the use of inexpensive and readily obtainable materials which are safe to handle and which clean the mercury to a de gree which meets the American Chemical Society standard of purity of mercury metal.

An object of the present invention is to provide a process which cleans contaminated mercury safely and inexpensively.

Another object is to provide a mercury cleaning process wherein essentially all contaminants are removed.

A further object is to provide a process wherein the cleansing action is improved by exposing a maximum surface area of the contaminated mercury to the treatments.

Another object is to provide a mercury cleaning treatment in which unusually simple and inexpensive means are employed for protecting the operator from escaping mercury vapors; this object being accomplished principally by maintaining the mercury submersed in an otherwise open container at all times during the treatments.

Yet another object is to provide a mercury cleaning process in which each of the treating agents is inexpensive and readily available; these agents further being entirely safe to handle to the extent that the user need not exercise any particular safety precautions.

A further object is to provide a mercury cleaning process utilizing weak basic solutions and weak acid solutions which are entirely safe to the operator.

Another object of the invention is to provide a mercury cleaning process utilizing a weak acid solution as one 3,113,018 Patented Dec. 3, 1963 'ice component of the process so that mercury does not combine therewith.

A further object of the invention is to provide a mercury cleaning process which utilizes a deflocculating cleaning agent, a Weak basic solution, and a weak acid solution to remove essentially all contaminants in the mercury without having any deleterious effect on the mercury or the operator of the process.

In the practice of the present invention a mass of contaminated mercury is introduced into a suitable container formed of a material which will not react chemically therewith, preferably of glass, plastic or porcelain. To this is added a treating agent solution which, most suitably, is a synthetic detergent, or the like, having the quality of removing hydrocarbon compounds such as oils and greases.

As indicated, the preferred solution for this initial cleaning treatment is a snythetic detergent or syndet as it often is called. The use of such a synthetic detergent is preferred because of its ready availability and relative harmlessness, as well as the fact that experimentation has established that such detergents are most effective in completely removing the oils and greases customarily found in contaminated mercury. On the other hand, it is appreciated that the cleansing action of other agents may be entirely efiective depending upon the contaminants present in the mercury. For example, other solvents in cluding soaps, alkalis and alkali salts, acids and acid salts, salts, or oxidizing or reducing agents may be used. It further is appreciated that there are a number of synthetic detergents which vary substantially in chemical composition and that particular detergents may be more appropriate under certain circumstances than others. In this regard, experience readily indicates to the user the detergent or other cleaning agent which is most appropriate.

With regard to the term detergent, it is recognized that, in its broadest sense, it encompasses all materials used in cleaning. More specifically, and in the sense used in the present specification and claims, the term detergent is limited to those surface-active agents which have, in addition to the property of lowering surface tension, the property of deflocculating soil and dirt clumps and keeping them in suspension to permit their being washed away rather than redeposited on the surface being cleaned. In further definition, the term synthetic detergents, or syndets, as used in the present specification and claims, applies only to the soapless detergents and it is believed that this distinction is generally recognized in the art. In other words, soaps are a special category of detergents, whereas the soapless detergents are known as synthetic detergents or syndets. The preferred process utilizes such as synthetic detergent although, as indicated, other detergent solutions and other cleaning agents may suffice under particular circumstances. In the specification and claims, the term cleaning agent is used to indicate the use of any appropriate cleanser such as conventionally may be used. Examples of such cleaning agents are sodium chloride, potassium sulfate, sodium carbonate and other similar compounds.

After the mercury has been immersed in the synthetic detergent or cleaning agent, the container then is vigorously agitated whereupon the mercury will be observed to separate into fine particles the size of which depends on the vigor and extent of agitation. Continued agitation reduces the mass of mercury to particles of substantially molecular size, thus exposing the greatest surface area to the cleaning action of the cleaning agent. During the agitation the hydrocarbon and other impurities are removed by the cleaning agent which together with these impurities then are washed away while constantly maintaining the mercury under water. The mercury is given two or three baths in this manner. It is to be noted at this point that most of the mercury will reunite upon thorough washing.

Next, the mercury is covered with a weak basic solution, such as calcium hydroxide, or the like, and allowed to stand with occasional stirring to break up the mercury. The mercury is then thoroughly washed with Water. It has been found most suitable to employ this weak basic bath to assure complete removal of the impurities. Further, it is important to note that the weak basic solution of calcium hydroxide is far preferable to other solutions such as the stronger potassium or sodium hydroxides. In fact, it has been found that the caustic action of these othersolutions, rather than being beneficial, causes the contaminants to become more intimately bound into the mercury to the extent that final cleaning must resort to strong and relatively dangerous acids, such as nitric acid.

Following the treatment with the weak basic solution, the mercury is treated with a weak or dilute acid solution which does not react with mercury and, as far as has been determined, an acetic acid solution is most effective. The mercury is allowed to stand, with occasional stirring, in the acetic acid solution, following which it is Washed and placed under distilled water in a suitable container for storage until needed. It is to be noted at this point that the small portion of mercury remaining broken-up will reunite when thoroughly washed following the acid solution treatment.

The use of acetic acid is to be contrasted with the prior art use of such compounds as cyanides or concentrated nitric acid, etc. Acetic acid not only is relatively harmless and easily available in the form of vinegar, but also it exhibits an improved cleansing action. In explanation, apparently a strong acid, such as nitric acid, reacts quickly not only with impurities, such as copper or lead, but also with the mercury itself. As a result, the mercury is pulled into solution along with the copper and lead impurities or with other impurities, such as zinc, iron, bis- 'muth, etc., that may be present. The difficulty seems to arise because the mercury so pulled into solution then is capable of recombining with the impurities and rendering cleaning even more involved. In contrast, the acetic acid apparently does not react with the mercury but instead exhibits a selective action in removing the impurities. Further, the concentration of the weal: acetic acid is not a critical matter as it may be in baths of nitric or other acids.

Atypical sample of contaminated mercury, before be ing cleaned, was tested and revealed the following results:

American Chemical Society evaporation test: Found Residue "percent" 0.042

Spectrographic determinations on residue:

Bismuth (Bi) percent 0.1 to 1 Cadmium (Cd) do 0.1 to 1 Tin (Sn) a do 0.1 to 1 Copper (Cu) Trace Lead (Pb) Trace Iron (Fe) Trace Magnesium (Mg) 1''r-ace Sodium (Na) Trace Calcium (Ca) Trace 1 Sample fails to meet ACS standard of purity for mercury metal.

A typical sample of contaminated mercury (about one pound) was cleaned in a Water solution of Cheer, a commercial detergent, by vigorously agitating the mercury in the detergent several times and then thoroughly washing oif with Water, while maintaining the mercury continuously under solution and under water. The sample was then placed in a flat'container, covered with a Weak basic solution of calcium hydroxide (0.02 N) and allowed to stand in this solution for forty-eight hours with occasional stirring. The sample was then thoroughly washed with water, placed in a container and covered with a 5% by Weight acetic acid solution for four days with occaanaere sional stirring. Finally, the sample was washed with distilled water and stored in a container containing distilled water. The above sample was tested and revealed the following results:

American Chemical Society evaporation test: Found Residue percent 0.0001

7 terials employed are both readily available and relatively harmless. The surface-active synthetic detergent Cheer may be found in any market and, as has been noted, the acetic acid is available in the form of vinegar. Equally important, however, these materials may be used Without any special precautions and even without the use of protective gloves or the like. In contrast, the strong caustic or concentrated acids of the prior art are quite dangerous and undesirable as well as being relatively difficult and expensive to obtain.

Because of the relative harmlessness of these agents, the present process can be conducted in an open tray or container rather than in the quite complete special apparatus required by the prior art. One advantage present in the use of the open tray is the ease with which it can be cleaned.

With further regard to the availability of the materials, it again should be noted that many detergents other than Cheer will suffice and, in fact, the cleaning has been accomplished with equal effectiveness by other equally common commercial detergents. In situations Where the synthetic detergent is not required, simple salts or other cleaning agents such as have been noted will be found effective.

Thus, it is seen that the present process has various advantages over the prior art methods which incorporate the use of strong basic and strong acid solutions to remove the contaminants in the mercury. Through the use of the cleaning deflocculating agent, the weak basic solution, and the weak acid solution, a cleaning process for mercury is provided which effectively removes contaminants such as oils and greases, as well' as compounds which combine with the weak basic solution and compounds which combine with the weak acid solution, for example, the metals. However, even though the mercury is cleaned of contaminants, the process involved does not have any deleterious effect on the mercury in that, through the use of the weak basic and the Weak acid solutions the mercury does not enter into chemical combination with the base or acid as it did in the prior art cleaning processes. Nor does the operator have to safeguard himself against the cleaning agents involved.

Obviously many modifications and variations of the present invention are possible in the light of the above teachings and it should be understood that within the scope of the appended claims, the invention may be practiced in other manners.

What is claimed is:

1. A process for cleaning a mass of contaminated mercury comprising submersing said mass in a surface-active detergent solution capable of removing grease and oil, agitating said submersed mass for exposing a maximum surface area of said contaminated mercury to the detergent action, washing said mass for removing said detergent solution and its entrained contaminants, submersing said washed mass in a calcium hydroxide solution, washing said mass for removing'said calcium hydroxide solution and its entrained contaminants, submersing said washed mass in an acetic acid solution, and again washing said acid-treated mass for removing residual acetic acid and its entrained contaminants.

2. A process for cleaning a mass of contaminated mercury comprising submersing said mass in a surface-active synthetic detergent solution capable of removing grease and oil, agitating said submersed mass for exposing a maximum surface area of contaminated mercury to the detergent action, washing said mass for removing said detergent and its entrained contaminants, submersing said Washed mass in a weak calcium hydroxide solution, washing said mass for removing said calcium hydroxide solution and its entrained contaminants, submersing said washed mass in an acetic acid solution, and again Washing said acid-treated mass for removing residual acetic acid and its entrained contaminants. 1

3. A process for cleaning a mass of contaminated mercury comprising submersing said mass in a surface-active detergent solution capable of removing grease and oil, agitating said submersed mass for exposing a maximum surface area of said contaminated mercury to the detergent solution, washing said mass for removing said detergent solution and its entrained contaminants, submersing said washed mass in a 0.02N calcium hydroxide solution,

References Cited in the file of this patent UNITED STATES PATENTS Re. 24,596 Deer Jan. 27, 1959 144,923 Randol et a1 Nov. 25, 1873 2,032,602 Stearns Mar. 3, 1936 2,440,456 Alley et al. Apr. 27, 1948 2,845,344 Sakowski -1 July 29, 1958 OTHER REFERENCES Moore: The Industrial Chemist, February 1932; pp. 63 and 64 relied on. 

1. A PROCESS FOR CLEANING A MASS OF CONTAMINATED MERCURY COMPRISING SUBMERSING SAID MASS IN A SURFACE-ACTIVE DETERGENT SOLUTION CAPABLE OF REMOVING GREASE AND OIL, AGITATING SAID SUBMERSED MASS FOR EXPOSING A MAXIMUM SURFACE AREA OF SAID CONTAMINATED MERCURY TO THE DETERGENT ACTION, WASHING SAID MASS FOR REMOVING SAID DETERGENT SOLUTION AND ITS ENTRAINED CONTAMINANTS, SUBMERSING SAID WASHED MASS IN A CALCIUM HYDROXIDE SOLUTION, WASHING SAID MASS FOR REMOVING SAID CALCIUM HYDROXIDE SOLUTION AND ITS ENTRAINED CONTAMINANTS, SUBMERSING SAID WASHED MASS IN AN ACETIC ACID SOLUTION, AND AGAIN WASHING SAID ACID-TREATED MASS FOR REMOVING RESIDUAL ACETIC ACID AND ITS ENTRAINED CONTAMINANTS. 